In case the metafile was imported from a PDF originally, then this
allows storing the PDF stream next to the graphic. This means that e.g.
in Writer choosing 'Save' from the context menu of the graphic can write
the original PDF stream, not the replacement metafile.

Change-Id: I4ab45d5af17fe46d7538df6d79d6b57ed163572a
Reviewed-on: https://gerrit.libreoffice.org/26628Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>